It has been found desirable in heat exchangers, particularly those used for condensers in refrigeration systems, to incorporate a serpentine tube configuration. The tubes are flat and are bent to form a plurality of straight passages connected by U-shaped bends. Preferably, two pre-bent extruded tubes are nested within one another and interconnected by fins (also called air centers) to form a tube and center style condenser. This style condenser uses tubes as a passageway for the refrigerant and the air centers attached outside the tubes increase the heat transfer. By nesting the two serpentine tubes together, a two passage serpentine condenser with increased performance is created.
The assembly of the air centers or fins between the tubes of the two passage condenser without special methods and equipment would be a difficult and time consuming process requiring hand insertion of the fins one at a time. Further, once the fins are assembled into the core, they must not move during subsequent handling or brazing. Steel banding straps are typically used to hold the core together until brazing is completed. In the case of the nested tube configuration, however, the banding pressures are not transmitted throughout the entire core. That is, the portions of the core having nested bends are relatively stiff and resist the externally applied pressure so that fins in such areas would be loosely held, at best. To some degree the same phenomenon occurs in a single serpentine tube configuration since the regions near each bend is stiffer than the rest of the core and the fins near the bend may not be held by the applied banding pressures.